Re: Extension/Extensibility examples in W3C Specifications

Bjoern Hoehrmann wrote:
> 
> Hmm. I am not sure whether this would be useful. What is an extension
> depends on context. Specifications are to say what is an extension and
> what is not. If they do not, an extension in their context is something
> (a language element) that is not defined in the relevant specifications.
> If you want a general definition, you would need to look at what is
> considered an extension by existing technologies and look at common
> properties. I'd say an extension is something for which the relevant
> specifications do not define processing consistent with the meaning of
> this very something.
> 

The OWL over RDF case has a very precise meaning for 'consistent'. The 
work went in to ensure that OWL semantics is consistent with RDF 
semantics, but that OWL when understood as RDF is 'incomplete' versus 
the same OWL when understood as OWL. In other words, if you understand 
OWL then you learn more, but nothing that you learn contradicts what you 
learnt with RDF alone.

A simple example is:

<http://example.org/> owl:differentFrom <http://example.org/>

is consistent as an RDF document, and inconsistent as an OWL document.
But there are no examples which are consistent as OWL and inconsistent 
as RDF.

So thinking about a rewording of your last sentence

"An extension is something which
defines additional processing that is not
part of the base specifications"

I think the word *additional* is crucial - an extension which negates 
the base specification is not an extension but a change. Of course, 
quite what constitutes "negating" is domain dependent.

Jeremy

Received on Wednesday, 5 May 2004 03:43:59 UTC